This invention relates to solid styrene-allyl alcohol based polyene compositions. More particularly, this invention relates to solid, solvent soluble curable compositions, comprising solid polyenes-liquid polythiols, method of preparing the same, as well as curing the solid polymer compositions in the presence of a free radical generator to solid, cross-linked, solvent-insoluble materials. More specificantly, this invention relates to solid photoresists and a method of preparing same.
It is known that polyenes are curable by polythiols in the presence of free radical generators such as actinic radiation to solid polythioether containing resinous or elastomeric products. In these prior art polyene-polythiol curable systems, either both the polyenes and polythiol were liquids, or one of the polymeric components was solid and the other liquid. Both liquid curable systems and the liquid-solid curable polymeric systems possess certain limitations and disadvantages. The use of curable liquid systems in preparation of photoimaged surfaces such as relief printing plates and photoresists have many undesirable features such as time consuming liquid coating operation which involves the use of cumbersome and additional apparatus, particularly expensive liquid dispensing equipment. A particular disadvantage of the liquid polymer systems is the resulting limited resolution during the photoimaging step, since it is necessary to maintain an air gap between the image, e.g., photographic negative and the liquid photocurable composition coated on a surface which is to be imaged in order to avoid marring the image and allowing its reuse.
Additionally, in the manufacture of certain printed circuits, when various photosensitive polymers are applied as liquid photoresists, they clog "thru-holes" in double sided or multi-layer printed circuits.
On the other hand, in the prior art solid polyene-liquid polythiol curable systems, the components are often incompatible, are not easily workable, or do not produce dry films, but only liquid curable compositions.
The novel solid curable polymer system of the present invention overcomes the numerous defects of prior art materials. The solid polyenes of this invention which are compatible with various liquid polythiols readily form solid curable compositions. These curable compositions can be compounded easily by mixing the solid polyenes and the liquid polythiols and be rapidly cured, particularly photocured in a solid state. The solid polyene-liquid polythiol mixtures are versatile photocurable compositions which are particularly useful in preparation of solid photoeresists, solid relief or offset printing plates, coatings and the like. The subject photocurable polyene-polythiol compositions readily form dry solid film materials which can be easily handled and stored prior to utilizing them in photocuring processes such as photoresist formation. The dry film polymer compositions can be readily laminated on a desired solid surface such as photoresist formation, selective portions of the solid photocurable polymer composition are photocured and insolubilized, thereby forming a protective coating which shows excellent adhesion to metal surface such as copper.
In accordance with this invention, a solid curable polyene containing at least 2 reactive carbon to carbon bonds per molecule can be readily prepared from styrene-allyl alcohol copolymer starting materials. These styrene-allyl alcohol copolymer based polyenes, when admixed with liquid polythiols, form highly reactive compositions which are capable of being photocured when exposed to actinic radiation in the presence of a UV sensitizer to insoluble polythioether containing materials which exhibit excellent physical and chemical properties. For example, photoresist coatings formed from cured polyene-polythiol compositions containing styrene-allyl alcohol copolymer based solid polyenes and liquid polythiols are capable of withstanding severe chemical environments employed in the printed circuit board manufacturing processes. The subject cured materials resist strongly acid etching solutions or highly alkaline conditions of electroless metal plating baths. The desirable characteristics of the cured materials make the polyene-polythiol curable compositions containing styrene-allyl alcohol copolymer backbone based solid, polyene particularly useful in both subtractive and additive circuitry applications.
Generally speaking, the novel solid curable composition is comprised of a solid polyene component containing at least 2 reactive carbon to carbon unsaturated bonds per molecule which is a reaction product of a copolymer of styrene-allyl alcohol and at least one unsaturated organic compound such as ene-acid or ene-isocyanate; and a liquid polythiol component containing at least two thiol groups.
The formation of such solid polyenes may be schematically respresented by the following non-limiting equation, wherein the unsaturated organic compound reactant is an ene-isocyanate having reactive allylic end groups as illustrated by a reaction product of one mole of 2,4-toluene diisocyanate with one mole of allyl alcohol: ##STR1## In the above equation, z is at least 2.
It is to be noted that in the above equation no attempt to show structural arrangement of the polymer is to the inferred.
Broadly, the operable polyene components of the solid curable composition are solid derivatives of styrene-allyl alcohol copolymers in which the reacting group is the hydroxyl functionality of the allyl alcohol portion of the copolymer. Operable solid polyenes include but are not limited to unsaturated ester and urethane derivatives of styrene-allyl alcohol copolymers.
As used herein, styrene-allyl alcohol copolymers refer to copolymers of an ethylenically unsaturated alcohol and a styrene monomer. Operable styrene-allyl alcohol copolymers are those containing from about 30 to 94 percent by weight of the styrene monomer, and preferably 60 to 85 percent by weight and correspondingly, from about 70 to 6 percent by weight of the ethylenically unsaturated alcohol, and preferably from about 40 to 15 percent on the same basis. In general, styrene-allyl alcohol copolymers having from about 1.8 to 10 percent hydroxyl groups, by weight, preferably 4 to 8 percent.
The actual hydroxyl group content of the aforesaid copolymers may not always conform to the theoretical content calculated from the relative proportions of styrene monomer and ethyleneically unsaturated alcohol, due to possible destruction of hydroxyl groups during copolymerization.
The styrene moiety of said copolymer may be styrene or a ring-substituted styrene in which the substituents are 1-4 carbon atom alkyl groups or chlorine atoms. Examples of such ring-substituted styrenes include the ortho-, meta- and para-, methyl, ethyl, butyl, etc. monoalkyl styrenes; 2,3- 2,4- dimethyl and diethyl styrenes; mono-, di- and tri-chlorostyrenes; alkylchlorostyrenes such as 2-methyl-4-chlorostyrene, etc. Mixtures of two or more of such styrene monomer moieties may be present. The ethylenically unsaturated alcohol moiety may be allyl alcohol, methallyl alcohol, or a mixture thereof. For the purposes of brevity and simplicity of discussion, the entire class of copolymers set forth in this paragraph shall hereinafter be referred to simply as styrene-allyl alcohol copolymers.
The styrene-allyl alcohol copolymers may be prepared in several ways. One operable method which yields styrene-allyl copolymer starting materials which are solid products is taught in U.S. Pat. No. 2,630,430. A more desirable method of copolymerizing the styrene and allyl alcohol components in a substantially oxygen-free composition, thus minimizing the oxidative loss of hydroxyl groups, is disclosed in U.S. Pat. No. 2,894,938.
Furthermore, the suitable styrene-allyl alcohol copolymers are generally commercially available materials.
The aforedescribed styrene-allyl alcohol copolymers are operable starting materials for the formation of the solid polyenes.
The polyenes of the subject invention have a molecular weight in the range of 332 to 20,000, preferably from 1200 to 10,000.
One group of operable polyenes containing styrene-allyl alcohol copolymer backbones are unsaturated urethane derivatives. These solid polyenes, i.e., unsaturated urethane derivatives of styrene-allyl alcohol copolymers may be represented by the general formula: ##STR2## wherein Q is a styrene-allyl alcohol copolymeric moiety remaining after n hydroxyl groups of a said styrene-allyl alcohol copolymer, have reacted to form n urethane, i.e., ##STR3## linkages; A and B are polyvalent organic radical members free of reactive carbon to carbon unsaturation and containing group members such as aryl, substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl and substituted alkyl containing 1 to 36 carbon atoms and mixtures thereof. These group members can be internally connected to one another by a chemically compatible linkage such as --O--, --S--, carboxylate, carbonate, carbonyl, urethane and substituted urethane, urea and substituted urea, amide and substituted amide, amine and substituted amine and hydrocarbon. Z is a divalent chemically compatible linkage such as ##STR4## --O-- and --S--, preferably ##STR5##
Preferred examples of operable aryl members are either phenyl or naphthyl, and of operable cycloalkyl members which have from 3 to 8 carbon atoms. Likewise, preferred substituents on the substituted members may be such groups as chloro, bromo, nitro, acetoxy, acetamido, phenyl, benzyl, alkyl and alkoxy of 1 to 9 carbon atoms, and cycloalkyl of 3 to 8 carbon atoms.
X is a member selected from the group consisting of:
a. --(CH.sub.2).sub.d --CR'=CHR
b. --O(CH.sub.2).sub.d --CR'=CHR
c. --S--(CH.sub.2).sub.d --CR'=CHR
d. --(CH.sub.2).sub.d C.tbd.CR
e. --O--(CH.sub.2).sub.d --C.tbd.CR
f. --S--(CH.sub.2).sub.d -C.tbd.CR
and mixtures thereof; and R and R' each are independently either a hydrogen or methyl radical, preferably a hydrogen radical; and d, p and q each are integers from 0 to 1; y is an integer from 1 to 10, preferably 1 to 5; m is an integer of at least 1, preferably from 1 to 4, and more particularly from 1 to 2, and n is an integer of at least 1, and preferably 2 or greater, and more particularly from about 4 to 10, with the proviso that when n is 1, y or m is at least 2.
As used herein, polyenes and polyynes refer to simple or complex species of alkenes or alkynes having a multiplicity of pendant or terminally reactive carbon to carbon unsaturated functional groups per averge molecule. For example, a diene is a polyene that has two reactive carbon to carbon double bonds per average molecule, while a diyne is a polyyne that contains two reactive carbon to carbon triple bonds per average molecule; a solid polyene which is a reaction product of a styrene-allyl alcohol copolymer having about 8 hydroxyl groups per average molecule and a reactive unsaturated monoisocyanate having one terminal reactive carbon to carbon double bond per average molecule is a complex polyene which contains in its structure 8 reactive carbon to carbon double bonds per average molecule. For purposes of brevity, all these classes of compounds will be referred to hereafter as polyenes.
In defining the position of the reactive functional carbon to carbon unsaturation, the term terminal is intended to mean that functional unsaturation is at an end of the main chain in the molecule. The term pendant means that the reactive carbon to carbon unsaturation is located terminal in a branch of the main chain as contrasted to a position at or near the ends of the main chain. For purposes of brevity, all of these positions are referred to herein generally as terminal unsaturation.
Functionality as used herein refers to the average number of ene or thiol groups per molecule in the polyene or polythiol, respectively. For example, a triene is a polyene with an average of three reactive carbon to carbon unsaturated groups per molecule, and thus has a functionality (f) of three. A dithiol is a polythiol with a average of two thiol groups per molecule and thus has a functionality (f) of two.
The term reactive unsaturated carbon to carbon groups means groups which will react under proper conditions as set forth herein with thiol groups to yield the thioether linkage ##STR6## as contrasted to the term unreactive carbon to carbon unsaturation which means ##STR7## groups found in aromatic nuclei (cyclic structures exemplified by benzene, pyridine, anthracene, and the like) which do not under the same conditions react with thiols to give thioether linkages. For purposes of brevity, this term will hereinafter be referred to generally as reactive unsaturation or a reactive unsaturated compound.
As used herein, the term polyvalent means having a valence of two or greater.
A general method of forming the urethane containing styrene-allyl alcohol copolymer based polyene is to react the styrene-allyl alcohol copolymer respresented by a general formula Q-(OH).sub.n, in which n is at least 1 and Q is as hereinbefore set forth; with at least one reactive unsaturated isocyanate of the general formula NCO-AZ.sub. p -B.sub.q -(X).sub.y ].sub.m in which the members A, Z, B, X and the integers p, q, y and m are as hereinbefore set forth.
The term reactive unsaturated isocyante will hereinbefore be referred to as an ene-isocyanate or an yne-isocyanate.
The reaction is carried out in the moisture free atmosphere at atmospheric pressure at a temperature in the range from about 30.degree. to 100.degree. C, preferably from about 40.degree. to 80.degree. C, for a period of about 10 minutes to about 24 hours. The reaction is preferably a one step reacton wherein all the reactants are charged together. The ene-isocyanate or yne-isocyanate is added in a stoichiometric amount necessary to react with the hydroxy groups in the styrene-allyl alcohol copolymer. The reaction, if desired, may be carried out in the presence of a catalyst and inert solvent. Operable non-limiting catalysts include tin catalysts such as dibutyl tin dilaurate, stannous octoate; tertiary amines such as triethylene diamine or N,N,N'N,'-tetramethyl-1,3-butanediamine, etc. Useful inert solvents include aromatic hydrocarbons, halogenated saturated aliphatic or aromatic hydrocarbons and mixtures thereof. Representative non-limiting examples include benzene, chlorobenzene, chloroform, 1,1,1-trichloroethane, 1,2-dichloroethane and the like.
Operable ene- or yne- isocyanates having the above defined general formula include, but are not limited to, simple monoeneisocyanates such as allyl isocyanate, 2-methallyl isocyanate, crotyl isocyanate, etc.
The aforementioned reactive unsaturated isocyanates are a group of compounds having the above general formula of operable ene- or yne-isocyanates wherein the integers p and q are 0 and m is 1. Thus, the urethane styrene-allyl alcohol copolymer based polyenes formed for these reactive unsaturated isocyanates may be represented by simplifyting the general formula for the polyenes to the following specific formula: ##STR8## wherein preferably y is 1 and n is 2 and the other members being as hereinbefore set forth.
Other operable ene- or yne-isocyanates are those prepared by reacting a polyisocyanate of the general formula A--NCO).sub.x, in which x is at least 2 and A is as hereinbefore set forth; with a reactive unsaturated alcohol of the general formula [(X).sub.y -B-]-OH in which B, X and y are as hereinbefore set forth.
The above polyisocyanate and alcohol reactants are added in such stoichiometric amounts that x-1 isocyanate groups react to give x-1 urethane linkages.
Operable non-limiting examples of starting polyisocyanate reactants include hexamethylenediisocyanate, tolylene diisocyanate, xylylene diisocyanate, methylenebis(phenyl isocyanate), 4,4'-methylene(cyclohexyl isocyanate), 1-methoxy-2,4,6-benzenetrisocyanate, 2,4,4'-triisocyanatodiphenylether, diphenylmethane tetraisocyanates, polyisocyanates having various functional groups such as N,N'N"-tris(isocyanatohexyl)-biuret or adducts of polyalcohols and diisocyanates which have at least 2 free isocyanate groups. Adduct of trimethylolpropane and 3 moles of toluene diisocyanate, is suitable.
Illustrative of the operable reactive unsaturated alcohols which may react with the polyisocyanates to give the desired eneisocyanate include but are not limited to allyl and methallyl alcohol, crotyl alcohol, crotyl alcohol, .omega.-undecylenyl alcohol, 2-vinyloxyethanol, vinylhydroxyethyl sulfide, propargyl alcohol, 1-allylcyclopentanol, 2-methyl-3-butene-2-ol. Reactive unsaturated derivatives of polyhydric alcohols such as glycols, triols, tetraols, etc., are also suitable. Representative examples include trimethylolpropane or trimethylolethane diallyl ethers, pentaerythritol triallyl ether and the like. Mixtures of various reactive unsaturated alcohols are operable as well. A suitable ene-isocyanate prepared by treating one mole of trimethylbenzene triisocyanate with two moles of trimethylolpropane diallyl ether. The resulting urethane containing ene-isocyanate is a polyene having four reactive allyl ether groups per molecule. Mixtures of various ene- or yne-isocyanates are operable as well.
Another class of solid polyenes operable in forming the solid curable polyene-polythiol system of the subject invention are esters of styrene-allyl alcohol copolymers. Similarly, these polyenes may be represented by the general formula ##STR9## wherein Q is a styrene-allyl alcohol copolymeric moiety remaining after removal of n hydroxyl groups from a said styrene-allyl alcohol copolymer thereby forming an ester linkage; the members A, B, and X and integers p, q, y, n and m are as hereinbefore set forth in the urethane containing styrene allyl-alcohol copolymer based polyene and k is an integer from 0 to 1.
A general method of forming these esters is to react the styrene-allyl alcohol copolymer respresented by the aforedefined general formula Q-(OH).sub.n ; with at least one reactive unsaturated monocarboxylic acid of the general formula: ##STR10## in which the members A, B and X, and the integers k, p, q, y and n are as hereinbefore set forth. The term reactive unsaturated carboxylic acid will hereinafter be referred to as an ene- and/or an yne-acid.
The esterification reaction may be carried out in a conventional manner in the presence of an acid catalyst, the water formed during the reaction being removed as an azeotrope.
Operable ene- or yne-acids include but are not limited to simple monoene-acids such as acrylic acid, methacrylic acid, vinylacetic acid, 5-hexenoic acid, 6-heptynoic acid, propiolic acid and the like.
These aforementioned reactive unsaturated acids are a group of acids having the above general formula of operable ene- or yne- acids wherein the integers p and q are 0, and m is 1. Thus the ester containing the styrene-allyl alcohol copolymer based polyenes formed from these reactive unsaturated acids may be represented by simplifying the general formula of the polyenes to the following specific formula: ##STR11## wherein, preferably, y is 1 and n is 2 and the other members being as hereinbefore set forth.
Other operable acids are those containing more than one terminally reactive unsaturated group in the molecule. These may be prepared by reacting a polycarboxylic acid of the general formula A-(COOH).sub.x, in which x is at least 2 and A is as hereinbefore set forth, with a reactive unsaturated alcohol of the general formula [(X).sub.y -B]-OH, in which B, X and y are as hereinbefore set forth.
The above polycarboxylic acid and alcohol reactants are added in such stochiometric amounts that x-1 carboxylic groups react to give x-1 ester linkages.
Operable polycarboxylic acids include but are not limited to dicarboxylic acids such as adipic, tartaric, succinic, terephthalic, etc.
Operable reactive unsaturated alcohol components are the same as described as being suitable in forming ene-isocyanates. As an example, a suitable ene-acid can be prepared by reacting one mole of trimethylolpropane diallyl ether with one mole of succinic anhydride in the presence of pyridine as a solvent. The resulting succinate product contains a free carboxylic group as well as two reactive allyl ether groups.
The liquid polythiols used herein for curing to a 3 dimensional network are simple or complex organic compounds having a multiplicity of pendant or terminally positioned --SH functional groups per average molecule.
On the average the liquid polythiol used for curing must contain 2 or more -SH groups/molecule and have a viscosity range of slightly about 0 to 20 million centipoises (cps) at 25.degree. C as measured by a Brookfield Viscometer. Operable polythiols used for curing in the instant invention usually have molecular weights in the range about 94 to about 20,000, and preferably from about 100 to about 10,000.
The liquid polythiols used for curing in the instant invention may be exemplified by the general formula R.sub.8 -- SH).sub.x where x is at least 2 and R.sub.8 is a polyvalent organic radical member free from reactive carbon-to-carbon unsaturation. Thus R.sub.8 may contain cyclic groupings and minor amounts of hereto atoms such as N, P or O but primarily contains carbon-carbon, carbon-hydrogen, carbon-oxygen, or silicon-oxygen containing chain linkages free of any reactive carbon-to-carbon unsaturation.
Certain polythiols such as the aliphatic monomeric polythiols (ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene-2,4-dithiol, and the like, and some polymeric polythiols such as a thiol-terminated ethylcyclohexyl dimercaptan polymer, and the like, and similar polythiols which are conveniently and ordinarily synthesized on a commercial basis, although having obnoxious odors, are operable but many of the end products are not widely accepted from a practical, commercial point of view.
One class of liquid polythiols operable with polyenes to obtain essentially odorless polythioether products are liquid esters of thiol-containing acids of the formula HS-R.sub.9 -COOH where R.sub.9 is a polyvalent organic radical member containing no reactive carbon-to-carbon unsaturation with polyhydroxy compounds of structure R.sub.10 -- OH).sub.x where R.sub.10 is a polyvalent organic radical member containing no reactive carbon to carbon unsaturation, and x is 2 or greater. These components will react under suitable conditions to give a polythiol having the general structure: ##STR12## where R.sub.9 and R.sub.10 are polyvalent organic radical members containing no reactive carbon-to-carbon unsaturation, and x is 2 or greater.
In the above formula for the polythiol ester R.sub.10 is a radical member remaining after removal of x hydroxyl groups from a polyhydric alcohol. R.sub.9 is a polyvalent, particularly divalent organic radical member selected from the group consisting of aryl, substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl and substituted alkyl groups containing 1 to 16 carbon atoms.
Preferred examples of operable aryl members are either phenyl or benzyl, and of operable cycloalkyl members which have from 3 to 8 carbon atoms. Likewise, preferred substituents on said substituted members selected from the group consisting of nitro, chloro, bromo, acetoxy, acetamido, phenyl, benzyl, alkyl, and alkoxy and cycloalkyl; said alkyl and alkoxy having 1 to 9 carbon atoms and cycloalkyl of 3 to 8 carbon atoms.
Operable polyhydroxy compounds are polyhydric alcohols such as various glycols, triols, tetraols, pentaols, hexaols, and the like. Non-limiting examples of polyhydric alcohols include simple aliphatic or cycloaliphatic polyols such as ethylene glycol 1,3 butanediol, trimethylolethane, 1,4-cyclohexanediol as well as halogenated derivatives such as 2-chloro-1,3-propanediol,2,3 -dichloro-1,4-butanediol and the like.
Additional operable polyhydroxy compounds are glycols formed from poly (alkylene oxides) such as polyethylene glycols, polypropylene glycols, polybutylene glycols or mixed poly(alkylene oxide) glycols. Preferably, the molecular weight of these polyols is within the range of 300 to 25,000 and especially within the range of 1500 to 6000.
Other suitable polyhydric alcohols containing oxygen atoms in the main chain are those formed by addition of an alkylene oxide, especially ethylene or propylene oxide to a triol or higher polyol. A specific example of a preferred polyol is an ethoxylated pentaerythritol.
Operable mercaptocarboxylic acids include but are not limited to thioglycollic acid (mercaptoacetic acid), .alpha.-mercaptopropionic acid, .beta.-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptoundecyclic acid, mercaptostearic acid, and o-and p-mercaptobenzoic acids. Preferably, .alpha. or .beta.-mercaptopropionic acid or thioglycollic acids are employed, since polythiol esters derived from these acids generally possess relatively low odor level and are compatible with the subject solid polyenes.
Specific examples of the preferred polythiols include but are not limited to ethylene glycol bis (thioglycolate), ethylene glycol bis (.beta.-mercaptopropionate), trimethylolpropane tris (thioglycolate), trimethylolpropane tris (.beta.-mercaptopropionate), pentaerythritol tetrakis (thioglycolate) and pentaerythritol tetrakis. (.beta.-mercaptopropionate), all of which are commercially available. A specific example of a preferred polymeric polythiol is polypropylene ether glycol bis (.beta.-mercaptopropionate) which is prepared from polypropylene-ether glycol (e.g. Pluracol P2010, Wyandotte Chemical Corp.) and .beta.-mercaptopropionic acid by esterification.
The preferred polythiol compounds are characterized by a low level of mercaptan-like odor initially, compatibility with the solid polyenes and after reaction, give essentially odorless polythioether end products which are commercially attractive and practically useful solid cured polymeric materials for both indoor and outdoor applications.
The polythiol esters may be prepared in a conventional manner, e.g., by reaction of the polyhydric alcohol component with the mercaptocarboxylic acid in the presence of an acid catalyst, the water formed during the reaction being removed as an azeotrope with a suitable solvent.
In summary, by admixing the novel solid styrene-allyl alcohol copolymer based polyenes with various liquid polythiols and thereafter exposing the solid mixture at ambient conditions to a free radical generator, a solid, cured insoluble polythioether product is obtained.
Prior to curing the solid polyene and liquid polythiol, components are admixed in a suitable manner so as to form a homogenous solid curable mixture. Thus, the polyene and polythiol reactants may be dissolved in a suitable solvent and thereafter the solvent can be removed by suitable means such as evaporation.
To obtain the maximum strength, solvent resistance, creep resistance, heat resistance and freedom from tackiness, the reactive components consisting of the polyenes and polythiols are formulated in such a manner as to give solid, crosslinked, three dimensional network polythioether polymer systems on curing. In order to achieve such infinite network formation, the individual polyenes and polythiols must each have a functionality of at least 2 and the sum of the functionalities of the polyene and polythiol components must always be greater than 4. Blends and mixtures of various solid polyenes and various liquid polythiols containing said functionality are also operable herein.
The solid compositions to be cured in accord with the present invention may, if desired, include such additives as antioxidants, accelerators, dyes, inhibitors, activators, fillers, thickeners, pigments, anti-static agents, flame-retardant agents, surface-active agents, extending oils, plasticizers and the like within the scope of the invention. Such additives are usually pre-blended with the polyene or polythiol prior to or during the compounding step. The aforesaid additives may be present in quantities up to 500 or more parts based on 100 parts by weight of the polyene-polythiol curable compositions and preferably 0.005-300 parts on the same basis.
The solid polythioether-forming components and compositions, prior to curing may be admixed with or blended with other monomeric and polymeric materials such as thermoplastic resins, elastomers or thermosetting resin monomeric or polymeric compositions. The resulting blend may be subjected to conditions for curing or so-curing of the various components of the blend to give cured products having unusual physical properties.
Although the mechanism of the curing reaction is not completely understood, it appears most likely that the curing reaction may be initiated by most any free radical generating source which dissociates or abstracts a hydrogen atom from an SH group, or accomplishes the equivalent thereof. Generally, the rate of the curing reaction may be increased by increasing the temperature of the composition at the time of initiation of cure. In many applications, however, the curing is accomplished conveniently and economically by operating at ordinary room temperature conditions.
Operable curing initiators or accelerators include radiation such as actinic radiation, e.g., ultraviolet light, lasers; ionizing radiation such as gamma radiation, x-rays, corona discharge, etc.; as well as chemical free radical generating compounds such as azo, peroxidic, etc., compounds.
Azo or peroxidic compounds (with or without amine accelerators) which decompose at ambient conditions are operable as free radical generating agents capable of accelerating the curing reaction include benzoyl peroxide, di-t-butyl peroxide, cyclohexanone peroxide with dimethyl aniline or cobalt naphthenate as an accelerator; hydroperoxides such as hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxides; peracid compounds such as t-butylperbenzoate, peracetic acid; persulfates, e.g., ammonium persulfate; azo compounds such as azobis-isobutyronitrile and the like.
These free radical generating agents are usually added in amounts ranging from about 0.001 to 10 percent by weight of the curable solid polyene-polythiol composition, preferably .01 to 5 percent.
The curing period may be retarded or accelerated from less than 1 minute to 30 days or more.
Conventional curing inhibitors or retarders which may be used in order to stabilize the components or curable compositions so as to prevent premature onset of curing may include hydroquinone; p-tert-butyl catechol; 2,6-di tert-butyl-p-methylphenol; phenothiazine; N-phenyl-2-naphthylamine; phosphorous acid; pyrogallol and the like.
The preferred free radical generator for the curing reaction is actinic radiation, suitably in the wavelength of about 2000 to 7500A, preferably for 2000 to 4000A.
A class of actinic light useful herein is ultraviolet light, and other forms of actinic radiation which are normally found in radiation emitted from the sun or from artifical sources such as Type RS Sunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps, tungsten halide lamps and the like. Ultraviolet radiation may be used most efficiently if the photocurable polyene/polythiol composition contains a suitable photocuring rate accelerator. Curing periods may be adjusted to be very short and hence commercially economical by proper choice of ultraviolet source, photocuring rate accelerator and concentration thereof, temperature and molecular weight, and reactive group functionality of the polyene and polythiol. Curing periods of less than 1 second duration are possible, especially in thin film applications such as desired, for example, in coatings, adhesives and photoimaged surfaces.
Various photosensitive, i.e., photocuring rate accelerators are operable and well known to those skilled in the art. Examples of photosensitizers include, but are not limited to, benzophenone o-methoxybenzophenone, acetophenone, o-methoxyacetophenone, acenaphthene-quinone, methyl ethyl ketone, valerophenone, hexanophenone, .alpha.-phenylbutyrophenone, p-morpholinopropriophenone dibenzosuberone, 4-morpholinobenzophenone, benzoin, benzoin methyl ether, 4'-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone, benzaldehyde, o-methoxybenzaldehyde, .alpha.-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene, thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]anthracen-7-one, 1-naphthaldehyde, 4,4'-bis(dimethylamino)benzophenone, fluorene-9-one, 1'-acetonaphthone, 2'-acetonaphthone, triphenylphosphine, tri-o-tolylphosphine, acetonaphthone and 2,3-butanedione, benz[a]anthracene 7,12 dione, etc., which serve to give greatly reduced exposure times and thereby when used in conjunction with various forms of energetic radiation yield very rapid, commercially practical time cycles by the practice of the instant invention.
These photocuring rate accelerators may range from about 0.005 to 50 percent by weight of the solid photocurable polyenepolythiol composition, preferably 0.05 to 25 percent.
The mole ratio of the ene/thiol groups for preparing the solid curable composition is from about 0.2/1.0 to about 8/1.0, and preferably from 0.5/1.0 to about 2/1.0 group ratio.
The solid curable polyene-polythiol compositions containing styrene-allyl alcohol copolymer based solid polyenes are used in preparing solids, cured cross-linked insoluble polythioether polymeric products having many and varied uses, examples of which include, but are not limited to, coatings; adhesives; films; molded articles; imaged surfaces, e.g., solid photoresists; solid printing plates; e.g., offset, lithographic, letterpress, gravures, etc., silverless photographic materials and the like.
Since the cured materials formed from the solid polyene-liquid polythiol compositions possess various desirable properties such as resistance to sever chemical and physical environments, they are particularly useful for preparing imaged surfaces.
A general method for preparing coatings, particularly imaged surfaces such as photoresists, printing plates, etc., comprises coating the solid curable composition on a solid surface of a substrate such as plastic, rubber, glass, ceramic, metal, paper and the like; exposing image-wise either directly using "point" radiation or through an image bearing transparency, e.g., photographic negative or positive or a mask, e.g., stencil, to radiation, e.g., U.V. light until the curable composition cures and cross-links in the exposed areas. After image-wise exposure, the uncured, unexposed areas are removed, e.g., with an appropriate solvent, thereby baring the unprotected surface of the substrate in selected areas. The resulting products are cured latent images on suitable substrates or supports. In case or preparing printing plates, e.g., a flexible relief plate wherein the susbstrate is usually a plastic material, the imaged product is ready for use. However, in other cases, e.g., in printed circuit manufacture or in chemical milling, the cured polymer composition acts as a photoresist.
The solid curable polyene-polythiol compositions of the subject invention are extremely suitable for use as a photoresist composition since (1) it adheres to the substrate firmly and readily on photocuring, (2) is resistant to the etching and plating environments for the substrate as well as soldering environments and (3) is easily removed by a solvent which does not affect the protected area.
Thus, in the preparation of an imaged surface by one operable photoresist process, the solid photocurable polyenepolythiol composition is coated or laminated onto an etchable solid surface, preferably a metal or metal clad substrate, as a solid, tack-free layer; exposed through an image bearing transparency to a free radical generator such as actinic radiation suitably in the wavelength range from about 2000 to 7500A or ionizing radiation to selectively cure the exposed portion of the composition, thus baring the metal beneath the removed uncured portion of the composition, optionally removing the exposed metal from the substrate to the desired depth and thereafter optionally removing the cured composition, thus leaving defined metal areas on the substrate.
In the printed circuit board manufacturing processes, the solid surface or board is usually electrically insulating substrate such as ceramic, thick plastic, epoxy, glass, etc., which can be clad with an etchable metal such as copper, aluminum, nickel, stainless steel and the like.
The above process illustrates the use of the solid photoresist in substractive circuitry applications, however, the subject solid photoresist compostions are very satisfactory for use in additive circuitry applications which utilize electroless metal plating processes which generally have highly caustic plating baths and thus require an extremely resistant photoresist material. Typical electroless metal plating baths, as well as conventional sensitizing and activating solutions utilized in additive circuit processes are disclosed in U.S. Pat. Nos. 3,546,009 and 3,573,973.
Various metals such as copper, nickel, gold, silver, tin, lead, etc., may be plated on metal clad substrates by conventional metal depositing techniques other than electroless plating, such as electroplating, chemical vapor deposition, flow soldering coating techniques and the like. The subject photocured resist composition are capable of withstanding the various metal depositing environments.
The solid film of photocurable composition can be formed by coating a solution or dispersion onto the metal cladding of a substrate and drying the layer by removal of the solvent by any suitable means, such as evaporation. The solid photoresist compositions may also be melted and suitably applied directly onto the metal surface of a metal clad substrate. Coating may be carried out by any of the conventional coating procedures such as spraying, dip coating, roller coating or curtain coating.
The photocurable resist layer has usually a dry coating thickness of about 1 mil, although it may range from 0.015 to about 5 mils or more, e.g., layers up to 10 mils are satisfactory.
In forming the solid photoresist composition comprised of the solid polyene and liquid polythiol, it is desirable that the photocurable composition contain a photocuring rate accelerator from about 0.005 to 50 parts by weight based on 100 parts by weight of the aforementioned polyene and polythiol.
It is to be understood, however, that when energy sources, e.g., ionizing radiation, other than visible or ultraviolet light, are used to initiate the curing reaction, photocuring rate accelerators (i.e., photosensitizers, etc.) generally are not required in the formulation.
When U.V. radiation is used for the curing reaction, a dose of 0.0004 to 6.0 watts/cm.sup.2 is usually employed.
The thickness of the metal or metal cladding on the substrates may vary from 0.1 mil to 20 mils, depending on the desired end use.